1. Field of the Invention
The invention relates to a device which can sort particles (sample) such as cells and blood corpuscles on the basis of scattering angle information of scatter.
2. Related Art
Flow cytometers, which is a one of kind of particle analyzer, include a cell sorter, a cell analyzer, and a particle analyzer (blood analyzer) which incorporate these devices. Such a flow cytometer is configured in the following manner. Particles flowing through or dropping from a flow cell are irradiated with light. Forward scatter, orthogonal scatter, or the like which is produced as a result of the irradiation is detected. Particles such as cells and blood corpuscles are sorted on the basis of the detected optical information.
It is known that, in forward scatter, the scattering angle varies depending on the kind of particles. Therefore, a device is proposed in which forward scatter is collected with being split into plural regions of different scattering angles, and forward scatter of each region is measured, thereby sorting particles. An example of such a device is disclosed in Unexamined Japanese patent publication HEI. 8-271509. In the device, cells contained leukocytes are optically detected so that cells of a small content are accurately sorted. FIGS. 8 and 9 show the configuration for detecting forward scatter in the disclosed device.
As shown in FIG. 9 including a section view of a flow cell used in the flow cytometer, the interior of the flow cell 2 has a structure wherein a sample tube 2c into which the sample (particles) flows is positioned in a center portion of a sheath fluid 2a which flows in a sheath-like manner and a sample flow 2b containing particles are formed in the tip end portion of the tube so as to be surrounded by the sheath fluid, thereby continuously supplying particles to a capillary portion. Since the capillary portion is irradiated with laser light a, a particle 7 passing through the portion function as the scattering source to produce forward scatters b, c, and d, orthogonal scatters e, f, and g (these scatters are directed to the back face of the sheet, and hence not illustrated), and back scatters h and i.
As shown in FIG. 8, the laser light emitted from the light source 1 is transmitted through the flow cell 2 and then blocked by an obscurator 11 which is immovably disposed. The forward scatter b, c, d or the like is converted into a collimated pencil of ray by a collimator lens 3 which is disposed in front of the flow cell 2, and then impinges on a forward-disposed mirror 4. A hole 4a is formed at the center of the mirror 4. Light of a small scattering angle in the forward scatter passes through the hole 4a and is then collected onto a first detector 6 by a first collecting lens 5. Light of a large scattering angle in the forward scatter impinges on the periphery of the mirror 4 to be reflected thereby so that the light pathway is changed by 90 deg., and is then collected onto a second detector 6' by a second collecting lens 5'. Each of the first and second detectors 6 and 6' is configured by a light/voltage converter element such as a photodiode, and converts received light into an electric signal corresponding to the intensity of the light. The signal is supplied to an analyzer 9.
In other words, the first detector 6 detects the intensity of forward small angle scatter having a small scattering angle, and the second detector 6' detects that of forward large angle scatter having a large scattering angle. The analyzer 9 calculates forward small angle scatter data and forward large angle scatter data from the incoming detection signals, and stores the calculated data. The analyzer calculates also 2-dimension coordinate data of the intensities of forward small angle scatter and forward large angle scatter. The analyzer 9 sequentially supplies the calculated forward small angle scatter data and forward large angle scatter data to an external display device (not shown) so that the data are displayed on a screen as a scattergram of a 2-dimension coordinate.
It is known that scatters produced by laser light irradiation have the following directional properties:
when the size of a particle is larger than the wavelength of the laser light, forward scatter is produced; PA1 when the size of a particle is at a similar degree as the wavelength of the laser light, forward and orthogonal scatters are produced; and PA1 when the size of a particle is smaller than the wavelength of the laser light, forward, orthogonal, and back scatters are produced.
In order to sort particles more correctly, therefore, an actual device is configured in the following manner. As shown in FIG. 9, for the forward scatters b, c, and d, an optical system 8 having a collimator lens 3, perforated mirrors 4, and collecting lenses 5, and detectors 6 for detecting the intensities of the scatters are disposed; for the orthogonal scatters e, f, and g also, an optical system 8 and detectors 6 are disposed; and, for back scatters h and i also, an optical system 8 and detectors 6 are disposed.
FIGS. 10(a)-10(b) shows another device described in Unexamined Japanese patent publication HEI 8-271059. In the device, light is not split into plural regions of different scattering angles, but split by using an optical fiber bundle 10. Namely, forward scatter emitted from particles in the flow cell 2 impinges on a light receiving face of the optical fiber bundle 10. In the light receiving face, as shown in FIG. 10(b), an optical fiber group 10a for receiving forward small angle scatter is disposed at the center, and an optical fiber group 10b for receiving forward large angle scatter is disposed in the periphery. As shown in FIG. 10(a), the emission side of the optical fiber group 10a is connected to the first detector 6, and that of the optical fiber group 10b to the second detector 6'. According to this configuration, scattering light entering the light receiving face of the optical fiber bundle 10 is supplied to either of the detectors 6 and 6' by a predetermined optical fiber group, in accordance with the scattering angle. In the same manner as the device of FIG. 8, the outputs of the first and second detectors 6 and 6' are supplied to the analyzer and then undergo a predetermined signal process.
However, the above-mentioned devices of the prior art have the following problems. In the device shown in FIG. 8, the optical system for enabling the detectors 6 and 6' to receive light requires the collimator lens 3, the perforated mirror 4, and the collecting lenses 5. Therefore, the number of parts is increased, and the adjustment of the optical system is complicated and cumbersome. Furthermore, the optical system occupies a large area, and hence miniaturization of the whole of the device is impeded. In a device such as shown in FIG. 9 in which the number of split regions is increased and orthogonal scatters and back scatters are to be further detected, perforated mirrors, the number of which is equal to (the division number-1), and collecting lens the number of which is equal to the division number are required. This causes the number of parts to be further increased, with the result that the above-mentioned problems become more serious.
In the device shown in FIGS. 10(a)-10(b), the collimator lens and the collecting lenses are not required, and the optical system requires only the optical fiber bundle. Even when the number of split regions is increased, it is necessary to increase only the number of optical fiber bundles. Unlike the device of FIGS. 8 and 9, the increase of the part number, and that of the occupied area are not large. However, the light receiving faces of optical fiber bundles must be concentrically arranged, and optical fibers must be collected in the unit of bundle. Therefore, a cumbersome process of routing optical fibers must be conducted. This causes the division number to be limited. Furthermore, the use of optical fibers brings a large loss. Specifically, a loss is produced when light passes through optical fibers, and light impinging on a clad is not transmitted. As a result, 50% or less of light impinging on the light receiving face of optical fiber bundle 10 shown in FIG. 10(a) can finally reach the detectors, thereby lowering the use efficiency of light.